The present invention relates generally to pressure equalization ports. More particularly, the present invention relates to a pressure equalization port to prevent vacuum seal in ultra low freezers.
A well known problem with refrigeration equipment is that room temperature air is exchanged with cold air in the freezer when the door is open. When the door is closed the room temperature air cools down, contracts, and causes a vacuum seal of the door. The door is then difficult to open until the pressure inside the freezer equalizes with the pressure outside the freezer.
Pressure equalization ports and other pressure equalization devices serve the purpose of reducing the time required to open a pressurized door for an ultra low freezer or other pressurized devices. This time differential can be from over 5 minutes without a pressure equalization port to 15 to 40 seconds with a pressure equalization port being present depending on pressure and port size. By reducing the amount of time for accessing the pressurized environment, users do not have to waste time and/or energy when opening pressurized doors. Pressure equalization ports therefore alleviate, to some extent, the need for pressurized doors to have bulky or cumbersome door opening mechanisms.
To improve operation, pressure equalization ports may also heat the incoming air within the pressure equalization port. This creates more of a pressure gradient between the cooler or unheated air on one side of the pressure equalization port which is at a lower pressure and the warmer outside incoming heated air which is at a higher pressure. This pressure gradient causes the air at higher pressure to circulate through the pressure equalization port and into the air at lower pressure until a balance or equalization of pressure is achieved. The introduction of heat within the pressure equalization port serves to expedite this process since pressure increases as temperature increases given a constant or fixed volume. Once pressure equalization occurs, any vacuum seal that may be present will be broken.
Numerous methods and devices have been developed to improve the pressure equalization process. For example, in the prior art (see FIGS. 1A and 1B) a pressure equalization port may include a stainless steel pressure equalization tube 1, a beater element 2, a valve/heater housing 3, and a split rubber valve 4. This pressure equalization port has several disadvantages. The split rubber valve 4 tends to stretch after several uses and therefore loses its seal. The heater element 2 extends into the pressure equalization tube 1 with a gap of over 0.15 inches between the heater element 2 and the stainless steel pressure equalization tube 1 resulting in a low heat transfer rate when heating the incoming high pressure air Axe2x80x2.
Furthermore, both the heater element 2 and the pressure equalization tube 1 extend and terminate inside the freezer cabinet 5 interior which clearly does not help in freezer performance, i.e., the heater element 2 is heating up the freezer""s interior (see FIG. 1A). Furthermore, the known thermal conductivity of the prior art stainless steel pressure equalization tube 1 is within the range of 9 to 30 (W/mxc2x7k) which is relatively low and results in the low heat transfer rate mentioned above.
This low heat transfer rate reduces the pressure gradient created between the low pressure end and the high pressure end of the pressure equalization port resulting in a slightly slower pressure equalization. Also, it should be noted that the heater element 2 may serve the purpose or function of preventing any accumulated condensation on the low pressure side of the pressure equalization port from clogging or interfering with air flow through the pressure equalization port. Therefore, it would be beneficial to use a high heat transfer material, such as aluminum or copper in conjunction with a heater.
While the currently developed pressure equalization ports provide advantages over previous systems, they still suffer drawbacks. The primary drawbacks are the uneven heating of the incoming air and extending both the heater and the pressure equalization tube into the freezer cabinet interior resulting in heating the freezer""s interior as well. Because of the thermodynamic characteristics of a freezer, any interjection of a heat source therein would lower the efficiency and/or performance of the freezer. A need still exists, therefore, for a pressure equalization port which can be used to prevent vacuum seal in an ultra low freezer and which will not affect overall freezer performance.
The foregoing needs have been satisfied to a great extent by the present invention wherein, in one aspect of the invention, a pressure equalization port is provided having a metal tube mounted within an insulated wall, e.g., an ultra low freezer cabinet wall. The tube having an outside end protruding outside the wall toward a high pressure area and an inside end mounted behind an insulating nylon bushing. The tube is terminated about 0.15 inches below the surface of the inside wall facing toward a low pressure area.
This pressure difference creates a pressure gradient which results in air flow from the high pressure area to the low pressure area. A vent is provided within the low pressure area and is mounted on the inside end of the metal tube. A heater surrounds the metal tube in order to supply evenly distributed heat transfer to the incoming air. Metal wool is placed within the metal tube at the inside end for additional heat transfer of the incoming air. The heating of the incoming air insures the flow of incoming and to impede the natural flow of air once pressure equalization is attained. By maintaining an environment above freezing, any collected condensation will not freeze thereby allowing the air to flow uninhibited.
In another aspect of the invention, a pressure equalization port is mounted within an insulated wall of a sealed chamber, having a non-conductive exterior tube, a conductive interior tube which is mounted within the non-conductive exterior tube. The conductive interior tube includes an end exposed to a high pressure area and an end exposed to a low pressure area. A heater is also mounted within the non-conductive tube and the heater surrounds the conductive interior tube, The insulated wall is exposed to a pressure gradient with the low pressure area on one side of the insulated wall and the high pressure area on the other. This pressure gradient causes air to flow from the high pressure area to the low pressure area through the conductive interior tube.
A method of equalizing pressure is yet another aspect of the invention, in which a non-conductive tube is mounted within an insulated wall of a chamber. Next, a conductive tube is mounted within the non-conductive tube. One end of the non-conductive tube and one end of the conductive tube are mounted substantially flush with an inside wall of the chamber. The conductive tube is then heated and an end of the conductive tube is exposed to a low pressure area and the other end of the conductive tube is exposed to a high pressure area, thereby creating a pressure gradient across the conductive tube which causes air to flow through the conductive tube from the high pressure area to the low pressure area.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology land terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.